全文获取类型
收费全文 | 14942篇 |
免费 | 741篇 |
国内免费 | 657篇 |
出版年
2024年 | 21篇 |
2023年 | 118篇 |
2022年 | 198篇 |
2021年 | 287篇 |
2020年 | 350篇 |
2019年 | 469篇 |
2018年 | 398篇 |
2017年 | 275篇 |
2016年 | 297篇 |
2015年 | 424篇 |
2014年 | 881篇 |
2013年 | 954篇 |
2012年 | 761篇 |
2011年 | 1015篇 |
2010年 | 836篇 |
2009年 | 667篇 |
2008年 | 675篇 |
2007年 | 719篇 |
2006年 | 577篇 |
2005年 | 544篇 |
2004年 | 536篇 |
2003年 | 500篇 |
2002年 | 401篇 |
2001年 | 279篇 |
2000年 | 271篇 |
1999年 | 263篇 |
1998年 | 259篇 |
1997年 | 262篇 |
1996年 | 216篇 |
1995年 | 213篇 |
1994年 | 200篇 |
1993年 | 185篇 |
1992年 | 150篇 |
1991年 | 156篇 |
1990年 | 126篇 |
1989年 | 145篇 |
1988年 | 119篇 |
1987年 | 99篇 |
1986年 | 98篇 |
1985年 | 122篇 |
1984年 | 247篇 |
1983年 | 192篇 |
1982年 | 205篇 |
1981年 | 154篇 |
1980年 | 147篇 |
1979年 | 139篇 |
1978年 | 49篇 |
1977年 | 45篇 |
1976年 | 43篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The fluorescence of the voltage sensitive dye, diS-C3-(5), has been analyzed by means of synchronous excitation spectroscopy. Using this rather rare fluorescence technique we have been able to distinguish between the slightly shifted spectra of diS-C3-(5) fluorescence from cells and from the supernatant. It has been found that diS-C3-(5) fluorescence in the supernatant can be selectively monitored at exc = 630 nm and em= 650 nm, while the cell associated fluorescence can be observed at exc= 690 nm and em = 710 nm. A modified theory for the diSC3-(5) fluorescence response to the membrane potential is presented, according to which a linear relationship exists between the logarithmic increment of the dye fluorescence intensity in the supernatant, In I/I°, and the underlying change in the plasma membrane potential, p=p-°p. The theory has been tested on human myeloid leukemia cells (line ML-1) in which membrane potential changes were induced by valinomycin clamping in various K+ gradients. It has been demonstrated that the membrane potential change, p,can be measured on an absolute scale.
Offprint requests to: J. Plasek 相似文献
82.
Klaus Hartfelder Heinz Rembold 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,160(6):617-620
Summary Juvenile hormone III content and ecdysteroid titer were analyzed for larval and pupal development of the stingless bee,Scaptotrigona postica depilis. Castespecific differences in juvenile hormone III content were detected at three developmental phases: at the transition from the fourth to the fifth larval stadium, in the spinning phase of the fifth larval stadium, and shortly after the imaginal moult. During the fifth larval stadium, juvenile hormone content closely reflects corpora allata activity. Juvenile hormone synthesis may thus be responsible for the elevated hormone titer in spinning-phase queen larvae, a phase of known sensitivity for induction of queen characters by exogenous juvenile hormone. For ecdysteroids, two phases of caste-specific differences were found: in the pre-pupal phase, and shortly after the imaginal moult. In both periods the titer in queens is distinctly higher compared to workers.Abbreviations
Im
imago 1 day after eclosion
-
L3, L4, L5
larval instars 3, 4, and 5
-
L5F1, L5F2
substages of feeding phase in fifth larval instar
-
L5S1, L5S2, L5S3
substages of spinning phase in fifth larval instar
-
PP1, PP2
substages of prepupal phase
-
Pw
white eyed pupa
-
Pp
pink eyed pupa
-
Pr
red eyed pupa
-
Pd
dark eyed pupa
-
Pdl, Pdm, Pdd
dark eyed pupa with progressive tanning of cuticle
-
RIA
radioimmunoassay 相似文献
83.
R Benali F Dupuit M Chevillard J Jacquot B Haye E Puchelle 《Biology of the cell / under the auspices of the European Cell Biology Organization》1991,73(1):49-56
Bovine tracheal gland (BTG) cells in culture show an epithelial-fibroblastoid transition after several passages. To investigate these BTG cell phenotype changes, we studied the effects of both the culture medium and passage number on the expression of epithelial cytoskeletal proteins and glandular serous cell markers. We also analyzed the intracellular cAMP level in the basal state and after adrenergic stimulation. Three culture media were used: 1) serum-free defined medium (SFDM); 2) medium supplemented with 2% Ultroser G; and 3) medium supplemented with 10% fetal calf serum (FCS). Using immunofluorescence microscopy, we showed that, in the first 4 passages whatever the culture conditions, BTG cells expressed immunoreactivities to cytokeratin filaments and desmoplakins I and II, whereas vimentin filaments were not detected. After four passages, BTG cells cultured in 10% FCS or 2% Ultroser G became progressively fibroblastoid and showed immunoreactivities to both vimentin and cytokeratin intermediate filaments. No immunoreactivity to vimentin filaments was observed on BTG cells cultured in a SFDM. Using biochemical analysis, we showed that basal levels of cAMP in cultured BTG cells and lysozyme secretion by these cells vary according to the culture medium and passage number. It was higher in BTG cells cultured in a SFDM compared to that recovered from cells cultured in medium supplemented with Ultroser G or FCS. Whatever the culture medium, BTG cells responded to stimulation by isoproterenol. However, the results of stimulation in a SFDM were higher than in Ultroser G or FCS supplemented medium. We conclude that the BTG epithelial cell organization and the regulation of biosynthesis of secretory proteins by these cells in culture depend on both the culture medium and passage number.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
84.
On artificial polyethylene membranes providing a thigmotropic signal, uredospores of the broad bean rust fungus Uromyces viciae-fabae differentiated a series of infection structures which in nature are necessary to invade the host tissue through the stomata. Within 24 h germ tubes, appressoria, substomatal vesicles, infection hyphae and haustorial mother cells were developed successively. Alterations in protein metabolism during infection structure differentiation of this obligate plant pathogen were analyzed in the absence of the host plant by high resolution two-dimensional polyacrylamide gel electrophoresis (2-DE) and silver staining. The norm pattern representing the 2-DE protein patterns of the whole developmental sequence of infection structures of U. viciae-fabae showed 733 spots. During infection structure differentiation 55 proteins were newly formed, altered in quantity, or disappeared. Major alterations in the protein pattern occurred during uredospore germination and when infection hyphae were formed. Uredospore germination was characterized by a decrease of acidic proteins and an increase mainly of proteins with isoelectric points ranging from weakly acidic to basic.Abbreviations 2-DE
two-dimensional polyacrylamide gel electrophoresis
- DAPI
4,6-diamino-phenylindol
- kDa
kilo Dalton
- pl
isoelectric point
- PMSF
phenylmethylsulfonyl fluoride
- SDS-PAGE
sodium dodecyl sulfate polyacrylamide gel electrophoresis 相似文献
85.
James B. Russell 《Archives of microbiology》1991,155(6):559-565
Glucose-limited, continuous cultures (dilution rate 0.1 h-1) of Streptococcus bovis JB1 fermented glucose at a rate of 3.9 mol mg protein-1 h-1 and produced acctate, formate and ethanol. Based on a maximum ATP yield of 32 cells/mol ATP (Stouthamer 1973) and 3 ATP/glucose, the theoretical glucose consumption for growth would have been 2.1 mol mg protein-1 h-1. Because the maintenance energy requirement was 1.7 mol/mg protein/h (Russell and Baldwin 1979), virtually all of the glucose consumption could be explained by growth and maintenance and the YATP was 30. Glucose-limited, continuous cultures produced heat at a rate of 0.29 mW/mg protein, and this value was similar to the enthalpy change of the fermentation (0.32 mW/mg protein). Batch cultures (specific growth rate 2.0 h-1) fermented glucose at a rate of 81 mol mg protein-1 h-1, and produced only lactate. The heat production was in close agreement with the theoretical enthalpy change (1.72 versus 1.70 mW/mg protein), but only 80% of the glucose consumption could be accounted by growth and maintenance. The YATP of the batch cultures was 25. Nitrogen-limited, glucose-excess, non-growing cultures fermented glucose at a rate of 6.9 mol mg protein-1 h-1, and virtually all of the enthalpy for this homolactic fermentation could be accounted as heat (0.17 mW/mg protein). The nitrogenlimited cultures had a membrane potential of 150 mV, and nearly all of the heat production could be explained by a futile cycle of protons through the cell membrane (watts = amperes x voltage where H+/ATP was 3). The membrane voltage of the nitrogen-limited cells was higher than the glucose-limited continuous cultures (150 versus 80 mV), and this difference in voltage explained why nitrogen-limited cultures consumed glucose faster than the maintenance rate. Batch cultures had a membrane potential of 100 mV, and this voltage could not account for increased glucose consumption (more than growth plus maintenance). It appears that another mechanism causes the increased heat production and lower growth efficiency of batch cultures. 相似文献
86.
Influences of the salt concentration on the fatty acid composition of Ectothiorhodospira species and other phototrophic purple bacteria have been analysed. Major fatty acids in bacteria of the genera Rhodobacter, Rhodopseudomonas, Chromatium, and Ectothiorhodospira were straight chain saturated and monounsaturated C-16 and C-18 fatty acids. Salt-dependent responses of all investigated bacteria revealed relations to their salt optima. Minimum values of C-16 and saturated fatty acids and maximum values of C-18 and unsaturated fatty acids were found at or close to the salt optima. Responses of Ectothiorhodospira mobilis upon changes in salinity were nearly identical, whether cells were grown in batch culture or in continuous culture with identical dilution rates at all salt concentrations. With increasing temperature, the fatty acid composition of Ectothiorhodospira mobilis and Ectothiorhodospira halophila strains showed decreasing portions of C-18 and of unsaturated fatty acids, while the contents of C-16 and saturated fatty acids increased. The results are discussed with respect to bilayer stabilisation and membrane fluidity.Abbreviations PC
phosphatidylcholine
- PG
phosphatidylglycerol
- CL
cardiolipin
- PE
phosphatidylethanolamine 相似文献
87.
Incorporation of fatty acids by Streptococcus mutans 总被引:1,自引:0,他引:1
Masaru Sato Hironori Tsuchiya Hideki Tani Kohji Yamamoto Ryozo Yamaguchi Hiroshi Nitta Nobutake Kanematsu Isamu Namikawa Nobuhiko Takagi 《FEMS microbiology letters》1991,81(1):117-121
In a series of investigations into the cariogenicity of Streptococcus mutans, we studied the incorporation of exogenous fatty acids with reference to glucosyltransferase secretion and membrane fatty acid changes. When cells were grown with different fatty acids, both saturated and unsaturated fatty acids were readily incorporated into the membrane lipids and were biotransformed and elongated preferentially to the longer 16- and 18-carbon-chain fatty acids. This incorporation and chain-elongation led to significant changes in fatty acids composition. By adding fatty acids to the medium, it was possible to appropriately modify the degree of unsaturation and the relative ratio between specific fatty acids in the membrane lipids of S. mutans. 相似文献
88.
Hideto Kuwayama 《生物化学与生物物理学报:生物膜》1988,940(2)
The effect of membrane potential on the activity of the ATP-dependent Ca2+ pump of isolated canine ventricular sarcolemmal vesicles were investigated. The membrane potential was controlled by the intravesicular and extravesicular concentration of K+, and the initial rates of Ca2+ uptake both in the presence and the absence of valinomycin were determined. The rate of Ca2+ uptake was stimulated by a inside-negative potential induced in the presence of valinomycin. The valinomycin-dependent stimulation was enhanced by the addition of K+ channel blocker, tetraethylammonium ion or Ba2+. The electrogenicity of cardiac sarcolemmal ATP-dependent Ca2+ pump is suggested from the increase of Ca2+ uptake by negative potential induced by valinomycin. 相似文献
89.
Synaptosomes isolated from the rat cerebral cortex were mixed with sonicated phospholipid vesicles and subjected to freezing-thawing to acquire giant proteoliposomes. Membranes of these giant proteoliposome could thus be studied using patch-clamp techniques. Single-channel currents were measured with the inside-out patch of the membrane, in KCl solutions. Three different potassium channels were detected and unit conductances were 15.1, 28.6 and 91.0 pS, respectively, in a symmetrical 150 mM KCl solution. All these channels are more permeable to potassium than to sodium ions, the permeability ratio being about 2:1. Tetraethylammonium ions blocked these channels. The gating of these potassium channels is independent of the membrane potential, Presumably, these channels play a role in the resting membrane potential of presynaptic nerve terminals. 相似文献
90.
Joseph A. N. Zasadzinski 《生物化学与生物物理学报:生物膜》1988,946(2)
Mixtures of sn-1 (
) and sn-3 (
) enantiomers of fully hydrated dipalmitoylphosphatidylcholine (DPPC) were studied with differential scanning calorimetry and freeze-fracture microscopy. The pretransition temperature of racemic mixtures of DPPC was 1.8 C° below that of either pure sn-1 or sn-3 enantiomers, which had similar pretransition temperatures. The main transition temperature of racemic mixtures was also depressed, but to a lesser extent, 0.8 C°. Freeze-fracture images of liposomes of sn-1, sn-3, and racemic mixtures of DPPC frozen from the Pβ′ phase showed well-defined ripples of wavelength 13 nm. Lipid stereoconfiguration had no effect on ripple wavelength, configuration or amplitude, or on the number and nature of surface defects. 相似文献